The present invention relates to a hub and a wheel for an at least partially muscle-powered two-wheeled vehicle and in particular a bicycle.
In the field of sports and also in competitions aerodynamically shaped bicycle components are increasingly employed to reduce drag during riding and to thus permit higher maximum and average speeds.
Other than spoke wheels, disk wheels are employed to reduce air drag. Disk wheels have the disadvantage, however, of causing perceptibly increased susceptibility to side winds.
Therefore, to reduce the air drag in spoke wheels, wheels have become known where the spoke bodies are flattened, being knife-like in structure and causing considerably reduced flow resistance in the riding direction. At the same time, the number of spokes tends to be reduced to still further reduce air drag.
With these flattened spoke bodies it is important for the spokes to be positioned in the direction of flow with their flattened sides since otherwise the flow resistance would not be reduced but inadvertently increased. A slight twist to the spoke bodies can already perceptibly increase air drag. Therefore hubs have become known which firmly receive the flattened heads of the spokes on two sides of a U-shaped groove where they are specifically guided to ensure a defined seat of the flattened spokes in operation.
The drawback of the known hubs in which the flattened spoke heads are firmly clamped and non-rotatably held in a fastening groove is that the hub only allows a precisely radial orientation of the knife-like spokes. The peripheral groove produced by way of an undercut in the hub body ensures a reliably firm seat only in the case of a precisely radial orientation of the spoke. Furthermore, the axial width of the groove must be matched precisely to the width of the flattened spoke head so as to attain security against twisting of the spokes received.
In typical wheels, a spoke is fastened to the hub at one of the two hub flanges provided axially outwardly. As a rule, the spoke is centrally fastened to the rim at the rim base. Rims with the spokes fastened to the rim flanks exist as well. In all of these cases, the spoke has a shape showing, other than a considerable radial element, also a significant axial element so as to bridge the axial distance between the fastening spot at the hub flange and the fastening spot at the rim.
Therefore, even in the case of spokes non-rotatably received in a fastening groove, alignment of the fastening groove should precisely match the alignment of the spoke to prevent the spoke from buckling. To this end, a three-dimensional, conical fastening groove would have to be inserted into the hub body. Only this would ensure a straight orientation of all the spokes showing no bending. However, this is too complicated and expensive when manufacturing such a fastening groove. Therefore, in the case of non-rotatably received, knife-like spokes, buckling in the spoke shape is accepted. This results in reduced stressability and in a spoke that is thicker than is actually required.
A considerable drawback of such a spoke accommodation in a fastening groove at the hub furthermore consists in that a purely radial alignment of the spokes is not possible for the transmission of driving force and also for the transmission of braking force e.g. via disk brakes. This is why the known systems are not suitable to be employed with the rear wheels of bicycles since these at least partially require an at least partially tangential spoke alignment to allow transmission of the torque applied.